1. Field of the Invention
The present invention relates generally to a method for resizing an image using the inverse discrete cosine transform (IDCT) and, more particularly, but not by way of limitation, to a method for enlarging an original image to an arbitrary resolution.
2. Description of the Related Art
A typical method for enlarging an image is to process the image in the pixel domain, wherein the number of pixels is increased by interpolating the pixels of the original image based upon the correlations of the pixels. This method, however, has several drawbacks. It requires a complicated algorithm for computing the correlation of each of the adjacent pixel values, and moreover, the quality of the increased-size image may be deteriorated by the interpolation operations.
Another method for enlarging an image is to process the image in the spatial frequency domain using the discrete cosine transform (DCT). An original image is divided into two-dimensional image blocks, for example, image blocks of size 8×8 pixels, and a DCT operation is performed on each of the image blocks to produce a DCT coefficient block having low and high spatial frequency components.
It is well known that the combination of DCT and quantization results in many of the frequency components being zero, especially the coefficients for high spatial frequencies because most of the energy in the original image is typically concentrated in low spatial frequencies. A common method taking advantage of this feature appends columns and rows of zeros to the high frequency area in the DCT coefficient block for increasing the size of the DCT coefficient block to integral multiples of 8×8, for example, 16×16 or 24×24. An inverse DCT operation on the increased-size DCT coefficient block leads to an enlarged image block.
The frequency-domain method is expected to gather popularity for resizing images because the algorithm is relatively simple and does not deteriorate the quality of the enlarged image. Methods for resizing images in the spatial frequency domain are disclosed in, for example, U.S. Pat. No. 5,737,019 issued Apr. 7, 1998, Korea patent application Ser. No. 1999-64158 filed Jul. 25, 1999, and Korea patent application Ser. No. 2001-49039 filed at Jun. 15, 2001.
While the methods disclosed in the referenced patents and applications show good results, there is a major limitation that an image cannot be enlarged to an arbitrary size and can only be enlarged to integral multiple times its original size. Also, adequate schemes for preventing possible distortions in an image after the image is enlarged to an arbitrary size have not been addressed yet.